This invention discloses an acousto-optic architecture for simultaneously obtaining time integration correlation and power spectrum analysis. The processor is designed to use commercially available Bragg cells and photodiode detector arrays, and should be realizable in fairly compact form. The correlator portion of the processor is a coherent, interferometric implementation, allowing attainment of the maximum possible bandwidth and dynamic range while achieving a time-bandwidth product of one million. The Bragg cell spectrum analyzer portion resolves a 30 MHz instantaneous bandwidth to 25 KHz, and can determine discrete frequency reception time to 10 .mu.s. The architecture is especially configured for spread spectrum signal detection, and a parallel combining scheme is disclosed to extend the instantaneous bandwidth of systems employing it.
The correlator portion of the processor is generically similar to the two beam surface acoustic wave time integrating correlator disclosed in U.S. Pat. No. 4,326,778, entitled "Acousto-Optic Time Integrating Correlator," and obtains the same maximum performance from a given detector diode array. In the patent, a highly efficient time integrating acousto-optic correlator which determines the time difference of arrival of the signals being correlated as well as the center frequency and bandwidth of the signals is disclosed. A surface acoustic wave delay line is provided with two counter-propagating surface acoustic waves with wavefronts tilted with respect to each other. Two laser beams are directed across the propagating waves with an angle of 4.theta..sub.B between them where .theta..sub.B is the Bragg angle, so that one beam interacts primarily with one propagating wave while the other beam interacts with the other wave. The modulated optical beams are directed to a time-integrating photodetector means which provides a signal output corresponding to the correlation function.
Another correlator is disclosed in U.S. Pat. No. 4,421,388, entitled "Acousto-Optic Time Integrating Frequency Scanning Correlator." An acousto-optic time integrating two-dimensional frequency scanning correlator is disclosed for cross correlating signals which are separated in frequency. Two coherent light beams which are derived from the same laser are fed across respective Bragg cells, one cell having the signal A(t) cos .omega..sub.A (t) propagating thereacross and the other cell having the signal B(t) cos .omega..sub.B t propagating thereacross. The respective output beams are compressed in the x-direction and expanded in the y-direction and are made incident on an acousto-optical correlator device having chirp signals counter-propagating thereacross. The optical output is fed to a time-integrating photodiode array which provides an output signal corresponding to the cross-correlation of A(t) and B(t).
In U.S. Pat. No. 4,225,938 to Turpin, entitled "Time-Integrating Acousto-Optical Processors," acousto-optical information processors employing a two-dimensional, time integrating architecture are disclosed. These three-product type processors are multi-purpose processors which can perform a variety of complex signal processing operations in two-dimensions, without requiring two-dimensional spatial light modulators. Typical of these processing operation are two-dimensional correlation, spectrum analysis, and cross ambiguity function processing. Some of the two-dimensional processing operations are made possible by the incorporation into a two-dimensional correlator of a distributed local oscillator, which may be implemented with mechanical-optical or electro-optical techniques.